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Reflections in coaxial connectors


Technics
Assembly and functional description

All connectors produce signal reflections at high frequencies. This is due to a minor variation of the connector impedance to that of the overall system. These irregularities have either inductive or capacitive behaviour depending on the operating frequency and the degradation of the performance at higher frequencies. The unmatched impedances can also be caused by a combination of internal dimension changes and tolerances, material and termination techniques. Different mating interfaces can also effect the overall system performance.
The reflection performance is commonly expressed as returnloss (a), S-Parameter (S-11), the Voltage Standing Wave Ratio VSWR (s) and the reflection coefficient (r) and all three correspond to each other mathematically: 

Return
loss
[-dB]

VSWR
s

Reflection
coefficient
r

1

17,3910

0,8913

2

8,27242

0,7943

3

5,8480

0,7079

4

4,4194

0,6310

5

3,5698

0,5623

6

3,0095

0,5012

7

2,6146

0,4467

8

2,3229

0,3981

9

2,0999

0,3548

10

1,9250

0,3162

11

1,7849

0,2818

12

1,6709

0,2512

13

1,5769

0,2239

14

1,4985

0,1995

15

1,4326

0,1778

16

1,3767

0,1585

17

1,3290

0,1413

18

1,2880

0,1259

19

1,2528

0,1122

20

1,2222

0,1000

21

1,1957

0,0891

22

1,1726

0,0794

23

1,1524

0,0708

24

1,1347

0,0631

25

1,1192

0,0562

26

1,1055

0,0501

27

1,0935

0,0447

28

1,0829

0,0398

29

1,0736

0,0355

30

1,0653

0,0316

Return
loss
[-dB]

VSWR
s

Reflection
coefficient
r

31

1,0580

0,0282

32

1,0515

0,0251

33

1,0458

0,0224

34

1,0407

0,0200

35

1,0362

0,0178

36

1,0322

0,0158

37

1,0287

0,0141

38

1,0255

0,0126

39

1,0227

0,0112

40

1,0202

0,0100

41

1,0180

0,0089

42

1,0160

0,0079

43

1,0143

0,0071

44

1,0127

0,0063

45

1,0113

0,0056

46

1,0101

0,0050

47

1,0090

0,0045

48

1,0080

0,0040

49

1,0071

0,0035

50

1,0063

0,0032

51

1,0057

0,0028

52

1,0050

0,0025

53

1,0045

0,0022

54

1,0040

0,0020

55

1,0036

0,0018

56

1,0032

0,0016

57

1,0028

0,0014

58

1,0025

0,0013

59

1,0022

0,0011

60

1,0020

0,0010

Due to the increased accuracy of cutting and solder termination of semi rigid cables, smaller impedance irregularities are achieved when compared with flexible coaxial cables. Connector styles also effect the reflection i.e. straight connectors generally produce a better performance than right angle versions. Therefore the reflection performance can vary within the same connector series dependent on style and cable.


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